Given the lack of vision of their leaders, it's very likely they won't.
My take is that Pentax will die soon or be bought off by someone else (and en up dying anyway).
Too many mistakes over the years.
A shame, because I think their bodies have among the best ergonomics.

What would they bring to the L-Mount? They don't even design their own lenses anymore: the new FF ones are rebadged Tamrons. In a year or two, all they will have left is their GR line, and a few specialty compacts.

What would they bring to the alliance? They have a history of providing very small lenses and compact bodies.
I don't know but I reckon that the L-mount is a (relatively) open system now similar to MFT.
Thus it may not be the question of whether there are benefits for the other members but there would be an obvious benefit for Pentax.